PhD ceremony Mr. G.G. Wybenga: Structural investigations into amino group transfer by two bacterial ß-aminotransferases and an aminomutase from plant

PhD ceremony: Mr. G.G. Wybenga

Dissertation: Structural investigations into amino group transfer by two bacterial ß-aminotransferases and an aminomutase from plant

Promotor(s): prof. B.W. Dijkstra, prof. D.B. Jansen

Faculty: Mathematics and Natural Sciences

The research presented in the thesis has focused on elucidating the 3D structures of three enzymes (MesAT, VpAT and PAM) at atomic resolution by means of protein crystallography. These enzymes catalyze amino group transfer, and have the ability to synthesize β-amino acids, which are building blocks of compounds with potentially useful activities (an example of which is taxol, an anti-tumor drug). The main insight that was obtained after elucidating 3D structures of MesAT, a pyridoxal-5’-phosphate (PLP) dependent β-aminotransferase from Mesorhizobium sp. LUK, which apart from β-amino acids also accepts α-amino acids, was that a β-amino acid binds in a reverse orientation within the MesAT active site as compared to an α-amino acid, and that this is facilitated by dual functionality of the enzyme’s active site carboxylate and side-chain binding pockets. The elucidation of 3D structures of VpAT, a pyridoxal-5’-phosphate (PLP) dependent β-aminotransferase from Variovorax paradoxus, allowed us to formulate an amino acid sequence motif that may be used to identify new aromatic β-aminotransferases from aminotransferase amino acid sequences. This may allow the identification of aromatic β-aminotransferases with new properties. The elucidation of 3D structures of PAM, a MIO (4-methylidene-imidazole-5-one)-dependent phenylalanine-2,3-aminomutase (PAM) from Taxus chinensis, which catalyzes a reversible isomerization reaction that leads to the conversion of (S)-α-phenylalanine into (R)-β-phenylalanine via trans-cinnamic acid, allowed us to explain the stereochemistry of the PAM-catalyzed reaction, and allowed us to explain how the MIO-group is formed from the three-amino-acid sequence motif Alanine-Serine-Glycine.